Showing papers on "Inertial measurement unit published in 1998"

Micromachined inertial sensors

Abstract: This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

Strapdown Inertial Navigation Integration Algorithm Design Part 1: Attitude Algorithms

Abstract: This series of two papers provides a rigorous comprehensive approach to the design of the principal software algorithmsutilized in modern-day strapdown inertial navigation systems: integration ofangular rateinto attitude, acceleration transformation/integration into velocity, and integration of velocity into position. The algorithms are structured utilizing the two-speed updating approach originally developed for attitude updating in which an analytically exact equation is used at moderate speed to update the integration parameter (attitude, velocity, or position) with input provided from a high-speed algorithm measuring dynamic angular rate/acceleration effects within the parameter update time interval [coning for attitude updating, sculling for velocity updating, and scrolling (writer’ s terminology ) for high-resolution position updating]. The algorithm design approach accounts for angular rate/specie c force acceleration measurements from the strapdown system inertial sensors as well as rotation of the navigation frame used for attitude referencing and velocity integration. This paper, Part 1, dee nes the overall design requirement for the strapdown inertial navigation integration function and develops direction cosine and quaternion forms for the attitude updating algorithms. Part 2 [Savage, P. G., “ Strapdown Inertial Navigation Integration Algorithm Design Part 2: Velocity and Position Algorithms,”Journal of Guidance, Control, and Dynamics (to be published )] deals with design of the velocity and position integration algorithms. Although Parts 1 and 2 often cover fundamental inertial navigation concepts, the material presented is intended for use by the practitioner who is already familiar with basic inertial navigation concepts.

Strapdown Inertial Navigation Integration Algorithm Design Part 2 : Velocity and Position Algorithms

Abstract: This series of two papers (Parts 1 and 2) provides a rigorous comprehensive approach to the design of the principal software algorithmsutilized in modern-day strapdown inertial navigation systems: integration of angular rate into attitude, acceleration transformation/integration into velocity, and integration of velocity into position. The algorithmsare structured utilizing the two-speed updatingapproachoriginallydeveloped for attitudeupdating;an analyticallyexact equation is used at moderate speed to update the integration parameter (attitude, velocity, or position)with input provided from a high-speed algorithmmeasuring rectiŽ ed dynamicmotionwithin the parameter update time interval [coning for attitude updating, sculling for velocity updating, and scrolling (writer’s terminology) for high-resolutionpositionupdating].The algorithmdesign approachaccounts for angularrate/speciŽ c force acceleration inputs from the strapdown system inertial sensors, as well as rotation of the navigation frame used for attitude referencing and velocity integration. The Part 1 paper (Savage, P. G., “Strapdown Inertial Navigation Integration Algorithm Design Part 1: Attitude Algorithms,” Journal of Guidance, Control, and Dynamics, Vol. 21, No. 1, 1998, pp. 19–28) deŽ ned the overall design requirement for the strapdown inertial navigation integration function and developed the attitude updating algorithms. This paper, Part 2, deals with design of the acceleration transformation/velocity integration and position integration algorithms. Although Parts 1 and 2 often cover basic concepts, the material presented is intended for use by the practitioner who is already familiar with inertial navigation fundamentals.

A low-cost GPS/inertial attitude heading reference system (AHRS) for general aviation applications

Abstract: An inexpensive Attitude Heading Reference System (AHRS) for general aviation applications is developed by fusing low cost ($20-$1000) automotive grade inertial sensors with GPS. The inertial sensor suit consists of three orthogonally mounted solid state rate gyros. GPS is used for attitude determination in a triple antenna ultra short baseline configuration. A complementary filter is used to combine the information from the inertial sensors with the attitude information derived from GPS. The inertial sensors provide attitude information at a sufficiently high bandwidth to drive an inexpensive glass-cockpit type display for pilot-in-the-loop control. The low bandwidth GPS attitude is used to calibrate the rate gyro biases on-line. Data collected during laboratory testing is used to construct error models for the inertial sensors. Analysis based on these models shows that the system can coast through momentary GPS outages lasting 2 minutes with attitude errors less than 6 degrees. Actual performance observed during ground and flight tests with GPS off was found to be substantially better than that predicted by manufacturer supplied specification sheets. Based on this, it is concluded that off-line calibration combined with GPS based in-flight calibration can dramatically improve the performance of inexpensive automotive grade inertial sensors. Data collected from flight tests indicate that some of the automotive grade inertial sensors (180 deg/hr) can perform near the low end of tactical grade (10 deg/hr) sensors for short periods of time after being calibrated on-line by GPS.

The role of dead reckoning and inertial sensors in future general aviation navigation

Abstract: Possible configurations for a general aviation autonomous navigation system are studied. Doubtless, an advanced GPS receiver is a "must have" system component. GPS has had some outages due to unintentional interference or even intentional jamming and aircraft should be able to navigate through such an event. Natural candidates for GPS backup are inertial sensors, magnetic compass, and air-speed sensors. All these sensors can be calibrated during GPS availability. Moreover, for dead reckoning systems, wind velocity can be estimated as well. This paper presents an original statistical model for wind variations that matches actual data very well. Using this model and a parametric family of inertial measurement sensors, horizontal position errors during a GPS outage are compared for a variety of configurations: a dead reckoning system, stand alone inertial sensors and inertial sensors integrated with the dead reckoning system.

F-16 flight tests of a rapid transfer alignment procedure

Abstract: This paper presents the results of an effort directed at developing and flight-testing an innovative rapid transfer alignment algorithm for inertially-guided air-launched munitions. The algorithm, referred to as RAP (Rapid Alignment Prototype), employs a 17-state Kalman filter designed to accurately align a weapon-grade Inertial Measurement Unit (IMU) relative to an aircraft-grade Inertial Navigation System (INS) within five seconds. The alignment procedure requires the pilot to execute only a brief wing-rock maneuver. No time-consuming heading changes or lengthy s-turns are required. The RAP Kalman filter achieves the rapid convergence time by recursively processing both velocity-match and attitude-match measurements at a 12.5 Hz rate to estimate and correct IMU velocity, attitude, and inertial sensor errors. Following laboratory and van testing at Eglin AFB, a series of F-16 flight tests were conducted. Flight test results demonstrated that the RAP filter achieved sub-milliradian alignment accuracy in less than 10 seconds. As further confirmation of alignment accuracy, IMU position error statistics were computed over a 100-sec post-alignment captive-carry trajectory. Test results indicated that the mean radial position error after 100-sec of unaided navigation was roughly 70 ft with an associated CEP of 61 ft. RAP's unprecedented alignment accuracy and reduced launch timeline provide a rapid-response capability for time-critical targets such as mobile launchers and troop emplacements.

Constrained navigation algorithms for strapdown inertial navigation systems with reduced set of sensors

Abstract: This paper develops a family of algorithms for low-cost strapdown inertial navigation system for land vehicles. Constraints on the motion of land vehicles are defined. They include constraints on vehicle's orientation relative to the Earth surface, and relationship between vehicle's attitude and its velocity direction. Navigation equations are derived that assume validity of these constraints on the vehicle's motion. Compared to standard strapdown inertial navigation, these algorithms reduce navigation errors in the presence of relatively high instrument noise, and at the same reduce number of required inertial sensors. Navigation errors are analyzed and used in an error model for the Kalman filter. Derived algorithms are applied to processing of experimental data.

Increased jamming immunity by optimizing processing gain for gps/ins systems

Abstract: A system and method for increasing jamming immunity in a GPS/INS system. The system includes a signal processor for receiving and down-converting GPS signals to a baseband frequency to provide I and Q (sine and cosine) signals. An integrate and dump operation is performed on the I and Q signals to provide GPS range and range rate residuals which are uncorrelated from sample to sample. A Kalman filter estimates navigation state corrections from the GPS range and range rate residuals. A NAV function, responsive to the output of the Kalman filter and range error and velocity errors signals, provides guidance information and signals for correcting at least one of earth centered earth fixed (ECEF) position, velocity, initial attitude and IMU alignment states which are dynamically calculated from the range and range rate measurements. A line of sight geometry function maps position and velocity vector information from the NAV function into geometric range and range rate scalar information and feeds the scalar information to the signal processor and circuitry to perform an integrate and dump operation.

Real-time IMU signal emulation method for test of Guidance Navigation and Control systems

Abstract: A real-time IMU emulation method for GNC method includes the step of receiving real-time flight data from a 6DOF flight simulator and generating simulated IMU electronic signals according to the IMU measurement modules and error modules defined by the user, and injecting said simulated IMU electronic signals into an on-board GNC system which causes the on-board GNC system into “thinking” that the vehicle is really moving. The on-board GNC system which is installed on the vehicle is motionless during the emulation test, so that the testing can be carried out in a laboratory or in an anechoic chamber facility and the IMU emulation can achieve the easy, effective, and least intrusive injection of emulated IMU signals into the INS computer. The present invention has features supporting the final integration of a developmental Guidance, Navigation, or Control (GNC) system installed into a vehicle. It assures testers that GNC avionics on-board vehicle work properly before and during a flight test. It also helps to debug on-board GNC avionics and verify system performance.

Coupled real time emulation method for positioning and location system

Abstract: A coupled real time emulation method for positioning and location system includes the steps of receiving real time trajectory data from a 6DOF trajectory generator and generating global positioning system simulated measurements and inertial measurement unit simulated electronic signals which are injected into an on-board integrated global positioning system/inertial measurement unit system. When the on-board integrated global positioning system/inertial measurement unit system is excited in dynamic operation, a performance thereof is able to be tested and evaluated as if carrying a real transportation test.

Using low-cost MEMS accelerometers and gyroscopes as strapdown IMUs on rolling projectiles

Abstract: Low-cost, micromachined, inertial sensors have been steadily emerging into the commercial marketplace. Some of these commercial off-the-shelf (COTS) sensors were evaluated for their insertion potential into military applications such as test and evaluation (T&E) and smart munition guidance. Performance requirements to provide time, space, position, and attitude information (TSPAI) and allow for navigation capabilities are fast approaching those needed, especially when integrated with a global positioning system (GPS) receiver. Artillery projectiles and rockets, instrumented with commercially available low-cost microelectromechanical systems (MEMS) accelerometers, spin sensors, and custom telemetry units, have been flight tested with good success. Test results suggest that many of these sensors are rugged enough for launch survivability and subsequent operation. Analysis of the accelerometer flight data shows good agreement with ground-based radar and other truth measurements. Ground tests of a MEMS gyroscope on a ballistic flight simulator have also been conducted. The results show promise for directly measuring a projectile's pitching and yawing behavior. This paper will present some of the test results and describe the challenges far using these devices as strapdown inertial measurement units (IMUs) on rolling projectiles.

Autonomous attitude acquisition for a stellar inertial attitude determination system

Abstract: A method and apparatus for autonomous acquisition of attitude in a stellar inertial spacecraft attitude system is disclosed. The present invention uses star trackers, an on-board star catalog, spacecraft steering and inertial sensors to determine spacecraft attitude. The present invention utilizes pattern match and pattern rejection methods and uses multiple stellar snap-shots in conjunction with spacecraft steering and spacecraft inertial measurements to acquire spacecraft attitude. Spacecraft inertial measurements are used to connect multiple stellar snap-shots to provide adequate star information that can be used to acquire spacecraft attitude. In an attitude determination system using star trackers, the star trackers may have a narrow field-of-view or few stars may be available for viewing. The present invention uses pattern matching and pattern rejection on different sets of stars, thereby allowing attitude acquisition when the number of stars in view is small.

Microtechnology for space systems

Abstract: Microelectromechanical systems (MEMS) are micron-to-millimeter size electromechanical devices that are fabricated using modified semiconductor batch-fabrication techniques We believe that MEMS technology will have a significant impact on future space systems by (1) reducing the size, mass, power, and cost of individual sensors and actuators used throughout spacecraft and launch vehicles and (2) ultimately reducing overall spacecraft size At the Aerospace Corporation, we are focusing on near and far-term applications of MEMS in space systems for reduced mass, improved performance, higher reliability, increased health and status awareness, and reduced life cycle costs Specific tasks include the development of micro-propulsion technology for microsatellites (1-to-100 kg mass) and nanosatellites (1-to-1000 gram mass), the development of a flight-qualifiable GN&C (guidance, navigation, and control) unit using a GPS receiver and MEMS inertial sensors, and the development of a MEMS-based wireless multiparameter sensor

MEMS inertial rate and acceleration sensor

Abstract: Development of the /spl mu/SCIRAS/sup TM/ (pronounced micro-Cyrus) multisensor for a period of over six years has produced a practical MEMS Inertial Measurement Unit (IMU). Using only three silicon sensors, a full-up IMU suitable for tactical grade navigation and guidance applications has been achieved. Iterative improvements in silicon sensor design and bulk micromachining processes have matured to the point where an IMU with an attractive price/performance ratio is now producible. This paper summarizes the design features and test results for an IMU with <100 deg/hr performance. Test results are shown for rate bias and acceleration bias over temperature. Production of this initial member of the /spl mu/SCIRAS product family begins in 1998 to support applications including guided artillery shells, technology insertion to decrease missile costs, navigation of remotely-piloted vehicles, dismounted soldier location devices and other navigation aids. The small size of this silicon multisensor and its ability to measure both angular rotation rate and linear acceleration provides a useful advantage in product packaging, cost, size, and system testing. The /spl mu/SCIRAS Inertial Sensor Assembly (ISA) is housed in a 2 cubic inch package weighing less than 5 ounces (140 grams) and requiring less than 0.8 W of power. Continuing development will lead to greatly improved performance on the order of 1 deg/hr at very low prices in high-volume production.

MEMS Inertial Rate and Acceleration Sensor

Abstract: Development of the /spl mu/SCIRAS/sup TM/ (pronounced micro-Cyrus) multisensor for a period of over six years has produced a practical MEMS Inertial Measurement Unit (IMU). Using only three silicon sensors, a full-up IMU suitable for tactical grade navigation and guidance applications has been achieved. Iterative improvements in silicon sensor design and bulk micromachining processes have matured to the point where an IMU with an attractive price/performance ratio is now producible. This paper summarizes the design features and test results for an IMU with <100 deg/hr performance. Test results are shown for rate bias and acceleration bias over temperature. Production of this initial member of the /spl mu/SCIRAS product family begins in 1998 to support applications including guided artillery shells, technology insertion to decrease missile costs, navigation of remotely-piloted vehicles, dismounted soldier location devices and other navigation aids. The small size of this silicon multisensor and its ability to measure both angular rotation rate and linear acceleration provides a useful advantage in product packaging, cost, size, and system testing. The /spl mu/SCIRAS Inertial Sensor Assembly (ISA) is housed in a 2 cubic inch package weighing less than 5 ounces (140 grams) and requiring less than 0.8 W of power. Continuing development will lead to greatly improved performance on the order of 1 deg/hr at very low prices in high-volume production.

Laser crosslink satellite attitude determination system and method

Abstract: A laser crosslink attitude determination system using the payload laser crosslinks as the principal attitude sensor and thereby eliminating the need for additional high-cost, high performance dedicated celestial body or inertial sensors to provide attitude information. The method and system establishes optical crosslinks among orbiting spacecraft for attitude control by performing a series of deterministic scans. The need for separate dedicated attitude sensors is minimized or eliminated by increasing the acquisition field of uncertainty and/or reducing the crosslink acquisition field of view.

A leveling algorithm for an underwater vehicle using extended Kalman filter

Abstract: Recently, the strapdown Attitude Reference System (ARS) became popular as an economic system for a small, light, low-cost system like an underwater vehicle. The ARS provides attitude information updated from the initial attitude. So, the initial attitude errors have a great effect on the ARS. In this paper, the leveling algorithm for compensating initial attitude errors using inertial sensors and a speed log is presented. The meaning of leveling in this paper is to acquire the two attitude angles of roll and pitch of the vehicle during its motion. The linear system model for the leveling is derived in order to apply extended Kalman filter (EKF) which is known to have many desirable properties. The simulation shows that the leveling algorithm using EKF is adequate by virtue of its property of decreasing attitude errors.

Utilization of GPS/MEMS-IMU for measurement of dynamics for range testing of missiles and rockets

Abstract: Missile and rocket test and evaluation centers currently rely on expensive, and at times inaccurate, radar and/or video tracking equipment to provide position, velocity, attitude, and time information of the missiles/rockets during flight test. Additionally, launch scenarios must be limited to locations where radar/video tracking equipment is able to track the missile/rocket through the entire flight. This paper presents an alternative approach using a small, low cost, integrated GPS receiver and MEMS-IMU embedded in the missile/rocket to provide (via telemeter link) accurate position, velocity, attitude, and time information of the missile/rocket during test flights. An introduction to the problem and the challenges faced in placing a GPS/MEMS-IMU on a small, high g, high roll rate platform is presented. A description of the integrated GPS/MEMS-IMU is presented along with simulated performance results. Finally, the benefits of using the integrated GPS/MEMS-IMU in the test and evaluation environment is discussed.

Precision hybrid navigation system for varied marine applications

Abstract: A need has long been established to provide low cost precise inertial and integrated navigation systems for seaborne applications. The adaptation of low cost, high volume electronics and inertial sensors from Kearfott missile and land products has enabled this need to become a reality. The development of a low power navigation system for guidance of Unmanned Underwater Vehicles used in applications such as deep salvage, oil and gas well head and pipeline laying and maintenance, sea bed mining, communications cable laying and maintenance, and scientific surveys is one example of this adaptive process. High speed patrol boats, corvettes, and other medium sized surface ships are further examples of applications that could benefit from the precise navigation and dynamic attitude information available from integrated systems of this type. All have stringent positioning requirements in order to define location as well as support of autopilot functions (attitude and/or heading control). Missions for this variety of applications may last many hours or even several days in duration, and may reach depths exceeding 5 km. By combining a low-cost but accurate Inertial Navigation System (INS), a Global Positioning System (GPS) receiver for surface operation INS alignment, and an accurate sonar Doppler Velocity Log (DVL) or Electromagnetic (EM) Speed Log for an in-water reference, with a sophisticated Kalman filter to combine these data in an optimal way, both surface and underwater navigation meeting these objectives can be achieved. Long term sea bottom position error growth rates of only a few meters per hour are possible.

High precision pointing system for airborne sensors

Abstract: The Position and Orientation System for Direct Georeferencing (POS/DG) is an off-the-shelf integrated GPS/inertial system designed specifically for airborne applications. It performs high quality measurements of position and orientation of an airborne sensor. Using an Inertial Measurement Unit (IMU) as the primary sensor, POS/DG achieves measurement accuracies of about 10 to 20 cm (RMS) in position and 20 to 30 are seconds (RMS) in attitude. POS/DG is used with airborne sensors requiring high-accuracy attitude measurements such as aerial cameras, multispectral scanners, laser scanners and digital cameras. For aerial cameras, POS/DG's performance enables the direct georeferencing of aerial photos to about 20 microns without aerial triangulation and ground control. The elimination of the aerotriangulation process translates to large savings in post-processing, data turn-around and flying time. The application of POS/DG to airborne photogrammetry is discussed and flight test results are presented.

Inertial sensor technology trends

Abstract: This paper presents the status of inertial sensor technology in underwater navigation applications, followed by a prediction of where inertial instrument technology is heading and in which applications the future sensor technologies will find a niche. Many kinds of sensors have been developed. The GPS is cheap and ubiquitous, but it is uncertain whether it would be continuously available in military scenarios.

Position and Orientation System for Direct Georeferencing (POS/DG)

Abstract: The Position and Orientation System for Direct Georeferencing (POS/DG) is an off-the-shelf integrated GPS/inertial system designed specifically for airborne applications. It performs high quality measurements of position and orientation of an airborne sensor. Using an Inertial Measurement Unit (IMU) as the primary sensor, POS/DG achieves measurement accuracies of about 10 to 20 cm (RMS) in position and 20 to 30 arc seconds (RMS) in attitude. POS/DG is used with airborne sensors requiring high-accuracy attitude measurements such as aerial cameras, multispectral scanners, laser scanners and digital cameras. POS/DG’s performance enables the direct georeferencing of aerial imagery to about 20 to 30 cm without aerial triangulation and ground control. The elimination of the aerotriangulation process translates to large savings in post-processing, data turn-around and flying time. The application of POS/DG to digital aerial cameras is discussed and flight test results are presented.

Strapdown inertial navigation system. Part 1 – Navigation equations

Abstract: Almost all aircraft are equipped with the Inertial Navigation Systems. The autonomous Inertial Systems are capable of calculating the navigational parameters of aircraft: position, velocity, and attitude, without external sources of information. In the paper the equations and algorithms of strapdown navigation system are derived and analysed. The research is focused on the calculation methods of the aircraft attitude.

Low dynamic IMU alignment

Abstract: IMU alignment is addressed by examining results from two different INS error modeling approaches using actual flight test data recorded from captive pod mounted IMU and reference INU. The emphasis of this paper is alignment during the aircraft's low dynamics ground operations before takeoff. The two MS error models used to produce the alignment results are based on computer frame and perturbation error models, and are formulated to use position observations in a transfer alignment Kalman filter algorithm. The use of position observations is consistent with other navigation aides such as GPS. Performance measures used to evaluate the two INS error models' results include: filter state convergence rates, IMU navigation solution heading compared to the reference MU heading, and post-alignment unaided navigation position error growth during manoeuvres after aircraft takeoff. For all three, the perturbation error model shows better results. The results suggest that alignment and aided navigation can be accomplished and sustained with a navigation filter algorithm which implements the perturbation error model without an alignment manoeuvre.

Integration of inertial information with vision

Abstract: Active vision systems can be used in robotic systems for navigation. The active vision system provides data on the robot's environment. In mobile systems the position and attitude of the cameras relative to the world can be hard to determine. Inertial sensors coupled to the active vision system can provide valuable information to aid the image processing task. In human and other animals the vestibular system plays a similar role. In this article, we explain our steps in the integration of inertial data with an active vision system. The active vision system has a set of stereo cameras capable of vergence, with a common baseline, pan and tilt. A process of visual fixation has already been implemented, enabling symmetric vergence on any selected point. An inertial system prototype, based on low-cost sensors was built. It is used to keep track of the gravity vector, allowing the identification of the vertical in the images. By performing visual fixation of a ground plane point, and knowing the 3D vector normal to level ground, we can determine the ground plane. The image can therefore be segmented, and the ground plane along which the robot can move identified. For on-the-fly visualisation of the segmented images and the detected points a VRML (virtual reality modelling languages) viewer is used.

GPS-aided navigation and unaided navigation on the joint direct attack munition

Abstract: The Joint Direct Attack Munition (JDAM) provides a low-cost accuracy enhancement to existing MK-83, MK-84, and BLU-109 weapons. Low-cost has been achieved through the use of commercial standards and high-volume production techniques. Accuracy improvements are achieved with a GPS-aided Inertial Navigation System (INS), an adaptive optimal guidance algorithm, an autopilot featuring a robust servo structure, and a tail actuator subsystem. Flight testing has demonstrated an impact uncertainty considerably less than the 13 meter Circular Error Probable (CEP) requirement in CPS-aided missions. This paper focuses on the JDAM navigator and Kalman filter algorithms that support both GPS-aided and unaided missions. The GPS-aided navigator consists of a tightly-coupled GPS/INS integration that supports both conventional and relative GPS operation. During GPS-aided operation, the JDAM Kalman filter is configured to estimate the basic kinematics states, calibrate critical inertial sensors, estimate GPS receiver clock errors, and estimate line-of-sight biases between the weapon and each NAVSTAR satellite tracked during the mission. JDAM also includes an unaided navigation mode that is used if GPS is denied. Unaided navigation relies on a transfer alignment algorithm to align the weapon's navigator to the carrier aircraft's navigator and to calibrate critical inertial sensors before release. Transfer alignment enhancements include senescence error estimation and an adaptive Kalman filter tuning algorithm that modifies filter process noise based on the weapon's vibration environment.

ICBM reentry vehicle navigation system development at Honeywell

Abstract: Development of navigation systems for reentry vehicles launched by ICBMs was initiated at Honeywell in 1977. Maintaining an accurate navigation solution through the spinning coast phase, and high acceleration reentry phase, of a reentry vehicle (RV) flight was enabled by the development of the Ring Laser Gyro. The original product, the Dormant Inertial Navigation System (DINS), provided navigation for the US Air Force Advanced Maneuvering Reentry Vehicle (AMaRV). The DINS, which employs strapped down technology, demonstrated the ability of tile Ring Laser Gyro to accurately measure the millions of degree's rotation experienced in the coast phase of flight. The laser gyro's minimal sensitivity to acceleration, and the excellent linearity of the Bell XI accelerometer, provided the needed reentry flight navigation accuracy. The DINS development was followed by the USAF Advanced Inertial Measurement Unit (AIMU) project. The next generation of the laser gyro, with advanced radiation hardening, was introduced on this program. In 1991, the Lockheed Missiles and Space Division (now the Lockheed Martin Missiles and Space Company) contracted Honeywell to develop an instrumentation package for the US Navy Trident system reentry vehicles. The Reentry Inertial Measurement Unit (RIMU) program presented unique design constraints based upon the need to identically match the physical properties of the predecessor IMU that was based upon spinning mass gyros and gimbaled platform technology. The Honeywell RIMU has performed reliably and accurately on several Trident flights. Through experience on the AMaRV, AIMU, and RIMU projects, Honeywell has achieved significant advancements in the real-time navigation software for strapped down technology. We have also developed the software tools to enable system and sensor configuration design trades for new missions. Additionally, our Post Flight Analysis software tool development, which started on the DINS program, has matured on the RIMU program. This paper presents the history of, and lessons learned during, the development of hardware and software for reentry vehicle navigation as conducted by Honeywell Space and Strategic Systems from 1977 through 1997. This experience provides the basis for a new generation of navigation systems for improved ballistic missile performance.

Vital Advanced Inertial Network

Abstract: Many aircraft sensors and weapons require accurate, local, time-varying inertial information relative to a principal reference, usually the main inertial navigation system. This data may be required during severe manoeuvres and despite other structural deflections due to aircraft aging, changing stores configurations, and fuel burnoff. Past solutions to this problem have included co-location, structural stiffening, or transfer alignment using high cost navigation grade inertial sensors. The Vital Advanced Inertial Network (VAIN) program sponsored by the Reference Systems Branch of the Wright Laboratory Avionics Directorate, is developing and testing an advanced inertial network to support precision targeting and weapon delivery under the influence of structural bending. This paper addresses some of the VAIN work and describes the sensor requirements for and performance of a transfer alignment based algorithm for compensating for aircraft flexure using low cost inertial sensors.

Real Time Calibration of Antenna Phase Errors for Ultra Short Baseline Attitude Systems

Abstract: Ultra short baseline attitude systems with base-lines under 0.5 meters are desirable for any application which requires a high level of integrity. The higher level of integrity is a direct result of the limited number of inte-ger ambiguities for shorter baselines. However, for ultra-short baseline attitude systems, phase errors translate into larger angular errors than they do in long baseline systems [1-8]. Many of the phase error sources such as carrier tracking loop noise and thermal noise can be filtered using inexpensive inertial sensors, however, other factors such as line bias variations and differences in antenna phase delay patterns generate slowly varying phase errors. Antenna phase errors are a function of line-of-sight to the satellites and vary at rates based on satellite movement and platform angular rate. Line bias errors are a function of temperature. These rates are generally too slow for inex-pensive inertial sensors to provide any filtering. Several methods for calibrating out these errors are presented.

An integrated GPS/INS navigation system for small AUVs using an asynchronous Kalman filter

Abstract: A small AUV navigation system (SANS) is being developed at the Naval Postgraduate School. The SANS is an integrated GPS/INS navigation system composed of low-cost, small-size components. It is designed to demonstrate the feasibility of using a low-cost inertial measurement unit (IMU) to navigate between intermittent GPS fixes. The paper reports improvements to the SANS hardware, latest testing results after compensating heading-dependent derivations in the TCM-2 compass measurements, and development of an asynchronous Kalman filter for improved position estimation.